1. Field of the Invention
The present invention relates to a zoom lens and an image pickup apparatus including the same, and more particularly, to a zoom lens suited for use in a broadcasting television camera, a cinema camera, a video camera, a digital still camera, and a silver-halide film camera.
2. Description of the Related Art
In recent years, a zoom lens having a wide angle of field, a high zoom ratio, and high optical performance is desired for use in an image pickup apparatus, such as a television camera, a cinema camera, a film camera, or a video camera. In particular, an image pickup device such as a charge coupled device (CCD) or a complementary metal oxide semiconductor (CMOS) used in a television or cinema camera as a professional moving image pickup system has a substantially uniform resolution over the entire image pickup range. Therefore, a zoom lens using the image pickup device is required to have a substantially uniform resolution from the center to the periphery of the screen. There are also needs for reductions in size and weight for an image pickup mode that places emphasis on mobility and operability.
In addition, a macro-photographing mechanism for enabling proximity photographing by moving a lens unit different from a focusing lens unit in an optical axis direction, and a flange back adjusting mechanism for adjusting a distance from a reference surface to which a lens mount is mounted to an image plane are highly requested for an interchangeable lens for a television camera or a movie camera.
As a zoom lens having a wide angle of field and a high zoom ratio, there is known a positive-lead type zoom lens in which a first lens unit having a positive refractive power and a second lens unit having a negative refractive power for variable power are arranged in order from an object side.
For example, in each of Japanese Patent Application Laid-Open Nos. 2002-169091 and 2007-78833, there is disclosed a zoom lens including, in order from an object side, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, a third lens unit having a positive or negative refractive power, and a fourth lens unit having a positive refractive power. In Numerical Embodiments of each of Japanese Patent Application Laid-Open Nos. 2002-169091 and 2007-78833, a lens unit movable for macro photography or flange back adjustment is provided within the fourth lens unit, which is arranged closer to an image side than a stop.
In order to achieve all, of a wide angle of field, a high zoom ratio, and high optical performance in the positive-lead type zoom lens, it is important to appropriately set an arrangement of the refractive powers of the lenses. In particular, because the lens unit closest to the image side plays a role of determining a size of all the lenses closer to the object side than the lens unit closest to the image side, in order: to achieve both of the optical performance and the reduction in size, it is important to appropriately set the lateral magnification of the lens unit closest to the image side. In addition, in order to mount the macro-photographing mechanism or the flange back adjusting mechanism to the positive-lead type zoom lens, the lens units, which are to be moved in an optical axis direction when the macro photography or the flange back adjustment is carried out, needs to have a moderate position sensitivity to back focus.
However, in the zoom lens disclosed in each of Japanese Patent Application Laid-Open Nos. 2002-169091 and 2007-78833, a relatively small-sized image pickup element (having a diagonal of 11 mm) for the television camera is supposed, and hence the lateral magnification of the lens unit closest to the image side is small. For this reason, if this zoom lens is applied to an image pickup element (having a diagonal of 25 mm or more) which has been increased in size in recent years, a lens diameter is increased in proportion to the increase in size of the image pickup element. In particular, in such a zoom lens that an angle of field at a wide angle end exceeds 70°, the increase in size of the lens unit closest to the object side becomes remarkable.